Butt-joining of steel bars

ABSTRACT

A TUBULAR SLEEVE IS PLACED OVER A PAIR OF ALIGNED ENDBUTTED STEEL BARS. THE STEEL BARS ARE COMPRESSED BY TOTALLY SURROUNDING JAWS TO COLD-FLOW THE TUBULAR SLEEVE AROUND THE STEEL BARS OVER THE ENTIRE SURROUNDED SURFACES THEREOF, PREFERABLY, THE TUBULAR SLEEVE HAS INTERNAL, INCLINED   SERRATIONS SO THAT, UPON COMPRESSION, AXIAL FORCES ARISE TENDING TO PRESS THE STEEL BARS TOWARDS EACH OTHER, STEEL WIRES MAY BE INSERTED PRIOR TO THE COMPRESSION STEP TO FURTHER INCREASE THE TENSILE STRENGTH OF THE JOINT.

Jan' 5,1971 s. GUTMANN 3,551,999

BT'l-'JOINING 0F STEEL BARS Filed Dec. 13, 1967 Y 2 Sheets-Sheet 1 l Jan- 5, 1971 y s', GUTMANN 3,55L999 BUTT'JOINING 0F STEEL BARSv Filed Dec. 13, 1967 2 Sheets-Sheet z FIG. i0

United States Patent O l 3,551,999 BUTT-JOINING F STEEL BARS Siegfried Gutmann, 45 Schwarzwaldstrasse, 76 Offenburg, Baden, Germany Filed Dec. 13, 1967, Ser. No. 690,214 Claims priority, application Germany, Dec. 14, 1966,

U.S. Cl. 29-517 10 Claims ABSTRACT 0F THE DISCLOSURE A tubular sleeve is placed over a pair of aligned endbutted steel bars. The steel bars are compressed by totally surrounding jaws to cold-flow the tubular sleeve around the steel bars over the entire surrounded surfaces thereof; preferably, the tubular sleeve has internal, inclined serrations so that, upon compression, axial forces arise tending to press the steel bars towards each other; steel wires may be inserted prior to the compression step t0 further increase the tensile strength of the joint.

The present invention relates to the butt-joining of steel bars and more particularly to butt-joining of structural steel members such as are used in connection with reinforced concrete, to provide a rapid and durable process of joining steel bars which can be carried out right at a construction site, with a minimum of expense, and still provide joints having full load-bearing strength both in tension, and in compression equal of that of the bars themselves.

Concrete construction frequently requires the butt-joining of steel bars, to extend bars of a given size or to interconnect them. Steel bars are usually delivered in length of 40 to 60 feet which, in construction, produce cut-offs of from 6 to 20 feet in length. For economical operation, the cut-offs should be used, Additionally, it is often necessary when Working with prefabricated reinforcedconcrete subcomponents, to provide for branchings or connections to the reinforcement bars. The joints must be rigid and must not deform under bending stresses.

Methods to make butt joints on reinforcement rods are known. These methods do not, however, have the required speed, simplicity, and economy required by modern construction techniques, and further the strength and durability of the butt joint is not perfect. For a long time, if has been known to provide friction fitting sleeves, having specially profiled shapes on the abutment surfaces. These sleeves require a considerable number of component parts, as well as work-time for their application. Additionally, the space requirement is large and extends beyond the longitudinal dimension of the sleeves themselves. Connecting sleeves having releasably gripping jaws, with clamping cones or wedges are expensive due to the necessity of providing threads, are comparatively sensitive to damage and require a plurality of coupling and clamping parts which are difficult to apply when work space is limited.

It has previously been proposed to utilize steel sleeves, without threads, and join butted ends by casting in molten metal, such as aluminum or zinc alloys, or tin/ zinc alloys. Adhesion by means of epoxy resin has been proposed. Using molten metal has the disadvantage that it can be utilized in practice only with upright sleeves, and further requires separate furnaces to melt the casting metal. The temperature of the molten Imetal is between 650 and 700 C., a temperature range unusual at structural sites. The ends of the steel bars, to be covered by the molten metal, must be meticulously dry and clean since, otherwise, the hot metal will spray and cause scaling or blow holes.

3,551,999 Patented Jan. 5., 1971 Also, considerable losses in the melting and casting metal occur, and thus such joints are quite expensive.

Connections made by adhesion with epoxy resins are even more sensitive to contamination by moisture or dirt. The heat-resistance of such connections is very low and further little is known about the properties of resins for long periods of time.

End-butted rods can be joined by electrical butt-welding, or may be overlapped and welded by ordinary arcwelding. If the bars are to be placed into tension, a specially formed sleeve is pushed over the butted ends, then electrically Welded to the butted ends of the rods. Such a process can, however, be carried out only in a shop and it is not possible to use it on bars already cast into cement. It is time-consuming to make the electrically welded connections, they require highly skilled and trained welding personnel and careful supervision and inspection. Additionally, the welded joints decrease the load carrying capacity of the rods, with a given diameter, by about 20% It has also been proposed to interconnect a pair of abutting steel rods by a cold-ow process. A tubular sleeve is slipped over the two rods, and pressed thereagainst. The known process is comparatively expensive, requires cornplicated internally toothed surfaces formed with clamping jaws and deformable inserts, which inserts supposedly cold-How upon compression of the sleeve. It has been found that substantial portions of the packing, intended to cold-ow, remains at the point between the rods, so that their load-bearing capacity is lost, and that the interior parts of the sleeves contact the rods only at points along the toothed inserts, leaving hollow' spaces which cannot accept any longitudinal forces. Such joints are, therefore, expensive and complicated and, since the endabutting rods do not have end-to-end Contact, commercially as well as technically uneconomical joints will be produced.

It has been proposed to cold-flow a tubular sleeve placed over bundles of reinforcement wires by a drawing or rolling process, in order to ycompletely surround the material of all the wires. Such a process requires an expensive drawing head, or drawing die, having ring-shaped notches to receive the bundle or strand of wires. The drawing process, during which the wires are pulled through a die after the drawing head is properly located, is not suitable for use on cement construction sites. Additionally, the conditions obtaining to join strands, or bundles could not be used as patterns to join opposing, abutting ends of reinforcement bars by mere radial pressure upon a tubular sleeve surrounding the two parts to be joined.

It is an object of the present invention to provide joints, and methods of applying them, to interconnect steelrods and particularly reinforcing rods in an economical and versatile manner, which can be carried out at actual construction sites and using only tools and processes usual at such sites.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, a tubular sleeve is placed over two, abutting rods. The inner surface of the sleeve, or the outer surface of the rod, has inclined serrations thereon, the direction of inclination being such that the rods are pressed to gether; for example, the rods, in accordance with custom, are cross-ribbed or have external projections. Radial pressure is applied to the sleeve across the entire cross-sec` tional area of the walls thereof, exclusively directed in a plane transverse to the axial direction of the sleeves and rods, by means of compression jaws, operating with such high pressure that the sleeve-material will flow practically at the entire circumferential surfaces adjacent the ends of the rods, and thus join the rods tightly and non-releasably together.

In accordance with a feat-ure of the present invention, the tubular sleeve has, at its inner surface, toothed regions, directed in opposite directions in such a manner that axial forces will arise tending to push the reinforcement rods together when the sleeve is compressed transversely to the axial direction. 'In order to further increase the tensile strength of the resulting junction, steel wires of high tensile strength bridging the butt-joint of the two rods can be inserted in the sleeve before compression.

According to a further feature of the present invention, each one of the rods has a half-sleeve pressed thereon having a pre-finished end, ush 'with the end of the rods; to provide a completely ush surface, if feasible, an additional surface preparation step may be used. The two rods, with their end-sleeves thereover, are then surrounded by one of the tubular sleeves which are cold-worked around rods and end sleeves.

The method of the present invention enables the production of a simple, strong joint which can be made directly at a construction site, by cold-flowing. The sleeve may be of any metal, for example aluminum, soft carbon steel, or pure iron, having each one of the rods to be joined inserted therein to half its length. The sleeve is then placed in a pressure tool, having a semi-circular recess therein (or, alternatively, a portable tool is placed around the sleeve, in situ). The half-round recess is preferably slightly smaller than the outer diameter of the sleeve. A similar counter die is placed against the rst work-die and the two dies are pressed together by means of a hydraulic press until the material of the sleeve completely covers and surrounds all surfaces of the ends of the rods. Pressures of from 50 to 250 tons are necessary. The junction can be used immediately after pressing, and both rods are connected together by a joint strong in both tension and compression.

In accordance with a different process, the radial forces are supplied by magnetic deformation, or by explosion pressure over liquid media.

Constructional steel according to the usual specification can be used, as well as the soft steels of reinforcement rods, the semi-hard steels and hard steels (see specifications DIN 1045, Groups I, IIa Illa, IIIb, IVa and semi hard steel of Groups II and III). The present invention is particularly applicable to ribbed reinforcement rods, for example cold-deformed (twisted) torsional steel. Self-hardening manganese and silicon containing constructional steel can also be butt-joined in accordance with the process of the present invention. The diameter of the rods to be joined is determined by the eventual use, customarily between 7 and 26 mm.

Rods of small diameter, for example 14 mm., can be joined usually by a single pressure step if sufficient compressive force is available. Larger rods may require more pressure steps, axially located one-behind-the-other. For example, pressure is applied in line with one end of the rods, and a second application of pressure at the opposite side of the other rod. The time duration of application of pressure, to provide for cold-liowing, is in the order of a minute. A manometer can be used as a measure to sense the compression of the sleeve.

The material to be used for the sleeves is chosen in accordance with the wall thickness left when passing over ribs or projections on the rods to be joined, as well as in dependence on the strength requirements of the joint, the availability of compressive force, and the eventual outer diameter of the sleeve. Steel sleeves only require 26 of the wall thickness for equal strength with respect to aluminum sleeves. The compressive force necessary when using steel is approximately less than that for aluminum. Rods of, for example, 1 inch diameter, joined in accordance with the present invention, may utilize a sleeve having an internal diameter of 30 mm., a length of about 4 inches and are made of aluminum. The outer diameter of the sleeve will be 66 mm, and, when utilizing two pressure steps, pressure of 200 tOnS Will be applied, Which Will correspond to a per-unit pressure of 7.5 to 8 t./cm.2. lf, however, steel is chosen as the material for the sleeve, an external diameter of 42 mm. su'lces. A single application of pressure of to 160 tons (corresponding to 6-7 t./cm.2) can be used. In both instances, the sleeve material will fully ilow between ribs or beads on the ends of the rods. A strain test was made; the strength of the junction is greater than that of the rods themselves, the break occurring in the rod beyond the junction. If, with larger diameters, the power of the press is insuicient, the pressure must be applied sequentially in order to retain the required per-unit pressure, for example four sequential pressing steps may be necessary, on two-each axially shifted points surrounding the rods to be connected.

The choice of the material for the sleeves can be influenced by the thermal loading and thermal resistance depending on building code requirements, for example in case of re. The limit for steel is at about 400 C., whereas the limit for aluminum is at about 200 C., or even less. Steel sleeves can be made of ordinary soft steel, that is soft carbon steel or over 0.1 percent C (specification DIN 2391). The sleeves may be made of precision tubes manufactured from seamless drawn carbon steel tubing. If pure iron is used, the wall thicknes of the sleeve has to be suitably chosen to compensate for the lower strength thereof. If high thermal loading is not expected, sleeves may be made of pure or alloyed aluminum, which can be pressed readily and which ows. A complete, tight junction is obtained upon application of pressure causing the aluminum to flow since, after metal had been worked to cold-flow, no spring-back will occur.

The joint made in accordance with the present invention provides for rods which are non-releasably connected together, that is the rods can transfer compression as well as tensile forces to their fullest extent. In order to provide for full tensile transfer of strength, the rods should have suitable shear surfaces in order to securely carry shear forces. At least, the surface should be roughened at the outside, in order to inhibit longitudinal shifting. The normal surface roughness of naturally hardened steel is suitable.

To provide for a tight joint of the rods against each other, the internal surface of the sleeves can be toothed, with the teeth directed inwardly in order to provide for axial forces against the rods upon application of radial forces. In accordance with a preferred embodiment of the invention, the pressure jaws may be formed with slightly double-conical outer surfaces in order to prevent sleeve material from flowing away from the butt joint, causing lateral shifting of the rods. The sleeve, itself, can be slightly conical as required. The sleeve may, in the region where the rods butt against each other, have a slight internal groove or recess in order to further prevent penetration of sleeve material between the rods and thus their separation.

If desirable, and if site conditions permit, the sleeves may be pre-heated in order to decrease the forces necessary by the pressure jaws.

The method according to the present invention may be used in order to join steel rods of any desirable length, for example, in reinforced cement construction, and before the reinforcing rods are built into the cement forms. Also, any kind of structural elements can be joined by means of butt-joints directly. The joints of the present invention have the advantage that the sleeve is simple, inexpensive, and largely insensitive against minor contamination by dirt or moisture. The transfer of force does not occur by adhesion, but rather by connection to the joining member. The junction can be made in any position, vertically, horizontally, or at any desired angle, and may be made by hand presses customary for clamping and joining of wire ropes. Such portable hand presses are particularly suitable for the joining of reinforcing rods directly at a construction site although, in shop operation, stationary hydraulic presses with suitable dies, corresponda ing to the various rod-diameters, would be preferred.

The structure, organization, and operation of the invention will now be described more specifically with reference to the accompanying drawings, wherein:

FIG. 1 shows a form of the butt joint connection in accordance with the invention, partly broken away;

FIG. 2 shows a sleeve used for making a connection, at the left-hand side before, and at the right-hand side after the compression step, in cross section;

FIG. 3 is a cross sectional view of rod to be compressed, with sleeve applied, and in the tool, prior to the pressure step;

FIG. 4 is a view similar to FIG. 3 at the end of the pressure step;

FIG. 5 is a partial longitudinal view, before the pres sure step, with an internally toothed sleeve;

FIG. 6 is a partially broken away longitudinal sectional view with inserted wires;

FIG. 7 is a partial longitudinal view of the sleeve, at the left-hand side before, and at the right-hand side after compression;

FIG. 8 is a transverse sectional view with inserted wires, and applied sleeve, before the pressure step;

FIG. 9 is a view similar to FIG. 8 after the pressure step; and

FIG. l is a partial broken, partial cross sectional longitudinal view of a pressure joint having a pair of internally applied auxiliary sleeves, and a covering outer sleeve.

Referring now to the drawings, where like parts have like reference numerals, and particularly to FIG. 1: A pair of reinforcing rods 1, 2, are joined by an external sleeve 3 applied thereover. FIG. 2 clearly shows the sleeve before, and after compression, the cross sectional area of the sleeve, and its shape, and the change thereof after compression `being clearly seen. The material of the sleeve tightly surrounds the entire circumference and the surface of the rods. FIGS. 3 and 4 illustrate the two pressure jaws 4, 5, having semi-cylindrical recesses y6, 7, the circumference of which is slightly smaller than the outer shape of the sleeve before the pressure step. After the pressure step, the surfaces of the grooves 6, 7 tightly surround the sleeve and the outer surface exactly conforms to the shape of the dies 4, 5, as seen best in FIG. 4. The internal surface of the sleeve is completely in contact, throughout its entire circumference, with the surface of the rods 1, 2. A small flash or ridge at the juncture of the two die parts 4, 5, is removed by the compression operation, it may remain in place, or may be removed by any other suitable tool.

FIG. illustrates a sleeve 8, having on both of its sleeve halves internal teeth 9 inclined in opposite direction in order to provide for axially directed forces in the direction of arrows 10 to press the ends of rods 1, 2 against each other. The sleeve is further formed with a central circular groove 11 which prevents penetration of metal into gap between the rods to be joined together.

Pressure is applied to the sleeve only in radial direction, with the pressure jaws moving only in radial direction. Thus, no space in the direction of the rod and beyond the extent of the sleeve itself is necessary for work tools, so that only a small space requirement is necessary and reinforcement rods extending but a short distance from already cast concrete can be spliced.

FIGS. 6 to 9 illustrate a pair of reinforcing rods 21, 22, and longitudinally extending steel wires 24, interconnected by means of a metal sleeve which is cold-flowed over the assembly of the rods 21, 22 and the steel wires 24. The steel wires, best seen in FIGS. 7 and 8, and loose in the sleeve before the compression process, tightly close the outer surface, and its profile during the compression step, as best seen by comparing the left and right halves of FIG. 7, and the cross sectional view of FIG. 6. The high tensile strength of steel wires prevents an internal shifting of the reinforcing rods under tension. After compression, they are completely enclosed by sleeve material which, throughout its entire length, passes between the various steel wires (see FIG. 9) and is in intimate contact with both the steel wires and the reinforcing rods.

The embodiment of FIG. l0 illustrates a pair of reinforcing rods 31, 32, on which initial half-sleeves 33, 34, are applied, by compression as previously described in connection with FIGS. 3 and 4. The end faces of the intermediate sleeves 33, 34, are preferably perfectly flat. Additionally, the end faces of the rods 31, 32 with the half-sleeves 33, 34 applied thereto can be worked to present perfectly at surfaces, which can readily be contacted without a gap (FIG. 10 shows such a gap for illustration only). An outer sleeve 36 is then slipped over the interior small sleeves 33, 34, and compressed thereover as previously described in connection with FIGS. l, 2, 3 and 4. The outer sleeve extends beyond inner sleeves 33, 34 to tightly interconnect the rods 31, 32 themselves. The outer ends of sleeves 33, 34 preferably taper to the diameter of the rods, as seen in FIG. 10. The thus formed shoulders prevent any possible opening of the compressed sleeves and readily transmit tensile stresses.

What is claimed is:

1. Method to interconnect a pair of abutting bars, each of said bars having an outer surface comprising placing a tubular sleeve of a material softer than said bars over the abutting end portions of the bars with the end faces of the bars in contact, said sleeve having an inner surface;

one of said surfaces being shaped to have inclined serrations, the inclinations of said serrations being directed to tend to press said bars together upon engagement of the sleeve with said bars;

and subjecting said sleeve, placed over the bars, to coldilowing, said cold-flowing step comprising completely enclosing the outer tubular circumference of said sleeve by compression means, applying force transversely to the axial direction of the sleeve under such pressure that the sleeve material will ow substantially over the entire surface of the bar portions within the sleeve, axial forces being applied by said inclined serrations during said compression step to tend to press the end faces of said bars together into tightly abutting relation while non-releasably tightly surrounding said bar portions.

2. Method according to claim 1 wherein the inner surface of said sleeve has serrations formed thereon inclined in opposite, facing direction so that, during the pressure step, axial forces will be applied by the serrations on said inner surface to said bar portions tending to press said bar ends together.

3. Method according to claim 1 wherein said step of cold-flowing comprises sequentially applying transverse pressure by said compression means; and moving said mean axially of said rods during sequential compression steps.

4. Method according to claim 1 wherein said sleeve is of aluminum.

5. Method according to claim 1 wherein said sleeve is iron or soft steel.

'6. Method according to claim 1 including the step of heating to below the recrystallization point said sleeve in advance of said cold-flowing step.

7. Method according to claim 1 including the step of inserting high tensile strength steel wire within said sleeve and extending for a length sufficient to bridge the abutting end faces of the bars prior to the cold-flowing step; and cold-flowing said sleeve over the assembly of bars and steel wires.

8. Method according to claim 1 including the step of applying a half-sleeve to each of said bars, said half-sleeve terminating flush with the end of said bar and having an outer surface; cold-flowing said half-sleeves, each, over the ends of said bars, each, said cold-flowing step comprising enclosing the outer surfaces of the half-sleeve by compression means moved transversely of the axial direction of the half-sleeve;

and placing the assembly of attached half-sleeves and bars within said tubular sleeve, said tubular sleeve being longer than both said half-sleeves together and extending therebeyond at either end;

and cold-owing said tubular sleeve over said assemblies of bars and half-sleeves.

9. Method according to claim 1, wherein said coldowing step comprises compressing said tubular sleeve by means of movable compression jaws, said compression jaws having a recess formed therein to accomodate said sleeve, said recesses, together, being slightly smaller than said tubular sleeve when in uncompressed state.

10. Method according to claim 1, wherein the inner surface of said sleeve is formed with a ring-groove in the region of the ends of said bars.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 9/ 1900 Great Britain. 7/1959 Great Britain.

JOHN F. CAMPBELL, Primary Examiner V. A. DI PALMA, Assistant Examiner U.S. Cl. X.R. 

